1. Field of the Invention
The present invention relates to radar systems generally and more particularly to radar systems which are relatively insensitive to jamming.
2. Description of the Prior Art
In the prior art, the concept of array-signal-processing has been developed and is described in the patent and other technical literatures. For example, in U.S. Pat. No. 4,034,376, entitled Radio Direction Finder with Array Element Signal Processing, the concept is described in a typical arrangement including a linear array of equally spaced elements. The array is passively operated; that is, it receives only. Radio frequency signals emanating from a mobile craft, either as a result of separate illumination or as a result of signals generated and radiated from the craft, provide signals at the antenna elements with a phase difference between successive elements in accordance with the angle of arrival of the RF pulses. Basically, the array is sequentially sampled (scanned) so that this phase or arrival time difference can be converted to a time-base or frequency-base signal. The array signal processing technique is applicable in multi-element linear or planar arrays, such as would commonly be employed as phased-array scanners.
Range and angle tracking are, of course, well-known, and those of skill in this art are familiar with the techniques. Angle tracking employing inertialess beam pointing techniques has come into prominence in recent years, and systems are known in which the rapidly variable beam pointing angle thus made possible can facilitate the time-shared tracking of a number of targets contemporaneously.
One of the problems in tracking a hostile airborne vehicle from a ground or shipboard position is the possible presence of a jammer or interfering source at an angle removed from, but relatively close to, the target of interest. Discrimination on the basis of frequency and so-called frequency hopping have been employed to ameriorate or dilute the effectiveness of such an interfering source. Frequently, however, broad-band interfering signals arriving on a "one-way" path cannot be adequately dealt with by such measures.
Radiation pattern tailoring or control is difficult and/or expensive to apply effectively, at least in accordance with classical approaches.
The manner in which the present invention provides a relatively simple arrangement for nulling an interfering source under the aforementioned circumstances will be evident as this descriptin proceeds. The accomplishment of the general objective of the invention will be recognized as this description proceeds.